The present disclosure relates to an additive for thermoplastic resins and to resin compositions containing such additives. In particular, the present disclosure relates to additives that enable improved flame retardant characteristics, heat deflection temperatures, and flow rates of thermoplastic resin compositions. The present disclosure also relates to a process for the preparation of a thermoplastic resin composition containing such additives.
Thermoplastic resins are used in different industries for use as materials for manufacturing electric parts and electronic appliances as well as for automobile parts. Additionally, thermoplastic resin compositions also have utility as such as adhesives, sealants, gels, automotives, cabling, electrical applications, aerospace, sporting equipment, electrical laminates, IC encapsulation materials, and the like.
Depending on the intended application, important properties for thermoplastic resin compositions include, but are not limited to, flame retardance, flowability, flexibility, Izod strength, heat distortion temperature, and the like. The standard test for flame retardancy is UL 94. In this test, a flame is applied repeatedly to vertically fastened test specimens. However, in some cases, exposing a polymeric composition to a flame leads to dripping of the flaming polymer material and ignition of the cotton wool mounted below a rod as defined in the test. This undesirable behavior can occur when large amounts of flameproofing agents are used in order to achieve short combustion times.
It is known in the art for example that addition of a halogen flame retardant can be used to impart flame retardancy to thermoplastic resin compositions. However, the use of halogen flame retardants results in the formation of halogen compounds, which can act as impurities in the resin compositions. It is also observed that halogen products are sometimes formed as thermal decomposition products, which can result in corrosion of the kneader, molding machine, mold, and other equipment used in the kneading and molding steps during extrusion. The use of halogen based flame retardants also suffers from the added disadvantage of formation of poisonous gas due to decomposition thereof.
Attempts have been made to avoid the use of halogen based flame retardants by using phosphorous-based compounds. For example, Japanese published application JP-A 55-82149 discloses a method for improving flame retardancy of thermoplastic polyester compositions comprising addition of red phosphorus or a phosphoric acid compound thereto. However, it is observed that the addition of red phosphorous, while avoiding the disadvantages of use of halogen based flame retardants, does not improve the flame retardancy. Moreover, the use of red phosphorus poses several handling problems. Red phosphorous poses the danger of dust explosion and also may emit smell or gas when processed in high temperature. It is also observed that red phosphorus alone does not provide the desired flame retardance and requires large quantities or combinations with other flame retardants.
In the fields where such flame-retardant resin compositions are used as, for example, electric and electronic parts, simplification of assembly and cost reduction have been desired, and it has been promoted to make parts integral or thinner. Therefore, materials used in these parts are required to show satisfactory flowability in molding in addition to maintaining high heat resistance and high flame retardance.
In general, the use of large amounts of flame retardant additive impacts on the heat deflection temperature and flow properties of the resin. Poor melt flow can impact the size and type of the part being prepared from thermoplastic resin and also further affect the equipment in which the composition is being processed.
Addition of organic phosphorus flame retardants to a thermoplastic resin compositions had been employed in an attempt to impart sufficient flame retardance. However, its use in some compositions leads to a considerable reduction in heat resistance. For example, polycarbonate resin compositions containing red phosphorus or stabilized red phosphorus also lack long-term heat stability. Moldings made thereof are often deformed on prolonged exposure to a temperature no higher than around 150xc2x0 C. Another problem faced in the use of phosphorous based flame retardants is that the compositions obtained thereby can suffer from poor molding processability due to low flowability. While the problem of flow can be overcome by molding at a high temperature, outgassing and decomposition can occur, which may contaminate the mold.
Other problems of using phosphorous compounds additives, e.g., resorcinol bis (diphenylphosphate) (RDP) or Bisphenol A-bis(diphenylphosphate)(BPA-DP), are that the cost overruns can be high. Attempts have been made to reduce the amounts of additives such as RDP or BPA-DP by using it in combination with other additives. For example, U.S. Pat. No. 6,359,043 describes the use of mica in combination with phosphorous additives.
Accordingly, it is desirable to provide a thermoplastic resin formulations, such as polyphenylene ether (PPE) or high impact polystyrene (HIPS), with high flow characteristics with reduced loadings of flow modifier to minimize the impact on heat deflection temperature (HDT )values, impact properties, and flame retardance. Moreover, it is desirable to reduce the amounts of the organic phosphorous compounds in the composition yet still effective to impart suitable flame retardance so as to minimize costs.
Disclosed herein is a flame retardant thermoplastic resin composition. In accordance with one embodiment, the thermoplastic resin composition comprises a thermoplastic resin: an organo phosphate in an amount less than or equal to about 20 parts by weight for every 100 parts by weight of the thermoplastic resin; and a polyhydric alcohol in an amount of about 0.25 to about 5.0 parts per weight for every 100 parts by weight of the thermoplastic resin.
In another embodiment, the thermoplastic resin composition comprises a thermoplastic resin comprising a polyphenylene ether resin, a high impact polystyrene resin or an acrylonitrile-butadiene-styrene resin; a resorcinol bis(diphenyl phosphate) compound in an amount less than or equal to about 20 parts by weight for every 100 parts by weight of the thermoplastic resin; and a polyhydric alcohol compound in an amount of about 0.25 to about 5.0 parts by weight for every 100 parts by weight of the thermoplastic resin.
A method for the manufacture of a flame retardant thermoplastic resin composition extrudate with improved flowability and Izod impact strength comprises mixing a thermoplastic resin comprising a polyphenylene ether resin, a high impact polystyrene resin, or an acrylonitrile-butadiene-styrene resin with an organo phosphate compound and a polyhydric alcohol compound to form a mixture, wherein the organo phosphate compound is in an amount less than or equal to about 20 parts by weight for every 100 parts by weight of the thermoplastic resin, and wherein the polyhydric alcohol is in an amount of about 0.25 to about 5.0 parts by weight for every 100 parts by weight of the thermoplastic resin; and extruding the mixture to form the extrudate.
The above described and other features are exemplified by the following detailed description.